This invention relates to the transmission of video pictures which contain depth information, and in particular to such a system which retains compatibility with monoscopic receivers.
Despite the recent advances in the field of higher definition, television cannot be a "window on the world" until it is able to convey some degree of depth information. Attempts have been made to transmit red/green anaglyph pictures to give a stereoscopic display, but this has resulted in complaints from viewers who do not possess the requisite spectacles. Clearly any attempt to transmit threedimensional (3D) pictures, must, to be practicable, transmit compatible monoscopic pictures.
The highest quality method of 3D image reproduction is represented by the hologram. It is, however, of little use to the broadcaster, requiring the illumination of the scene with at least partially coherent light or, if image scaling is required, microwaves or X-rays (depending on the direction of scaling). Even if the problems of image scaling could be overcome by some form of signal processing, the phenominal bandwidth of a "raw" hologram, of the order to 100 Gbit/s, would present considerable problems of redundancy removal, channel coding and transmission. Nevertheless, as a display the hologram is unsurpassed, conveying an air of realism far beyond that achievable with other methods.
Stereoscopy on the other hand is relatively simple to handle, using available light, and requiring only twice the original bandwidth even if no attempt is made at redundancy removal. It is also amenable to bandwidth reduction. So stereoscopy is the best choice for both studio and transmission. Where steroscopy does not excel is in the display, since most systems require polarising glasses and the picture is unwatchable without them.
U.S. Pat. No. 3,674,921 describes a method of transmitting a stereoscopic signal over a reduced bandwidth by transmitting a monoscopic signal and a difference signal. The difference signal, of 0.5MHz bandwidth, is derived from the high frequency difference between two source signals. Most of the stereoscopic information is concentrated in the high frequency areas of the difference signals, but even by transmitting only this part of the difference signal, information not necessary to stereoscopic reception is transmitted, and further bandwidth reduction is difficult.